1. Field of the Invention
The present invention relates generally to technology employed to brake vehicles, and particularly to that employing auxiliary equipment to increase engine brake to brake vehicles.
2. Description of the Background Art
An automatic transmission automatically shifting speed is conventionally known. When a vehicle having such an automatic transmission mounted thereon, and coasting with the accelerator off is decelerated, the transmission can downshift. If the transmission has downshifted, and the current speed is shifted, the engine thereafter has an increased rate of rotation, and engine brake contributes to increased braking force. This changes deceleration between before and after the current speed is changed, and the vehicle's occupant(s) may feel physical impact.
Japanese Patent Laying-open No. 10-236290 discloses a brake control device for vehicles that is capable of preventing shift shock in downshifting with power (or the accelerator) off. As described in the publication the brake control device controls a vehicle having an automatic transmission mounted on the vehicle and a brake device applying braking force to the vehicle. The brake control device includes a downshift predictor predicting whether the automatic transmission downshifts, a braking force application controller driven by information received from the downshift predictor to automatically apply braking force to the brake device after such prediction is made and thereafter the transmission has completely downshifted until a prescribed period of time elapses, and a limiter limiting an amount of braking force applied by the braking force application controller when the transmission is downshifting. When the downshift predictor predicts that the transmission downshifts, the controller incrementally applies braking force to increment deceleration and when the transmission starts to downshift the limiter simultaneously decrease an amount of braking force applied and when the transmission has completely downshifted, the interrupted application of braking force is resumed and decremented.
In the brake control device as described in the publication when a prediction is made that the automatic transmission downshifts, the braking force application controller applies braking force. When the transmission is actually downshifting the limiter limits braking force applied to a reduced amount. Thus, before the transmission starts to downshift, the vehicle is decelerated, and when the transmission downshifts, increased engine braking caused by a difference in rate of rotation attributed to a difference in gear ratio between before and after a gear is shifted, can be prevented, and between before and after the gear is shifted the vehicle can have a minimized difference in deceleration. This can provide significantly reduced shift shock caused by engine brake in downshifting and thus suitably prevent the vehicle's occupant(s) from feeling uncomfortable in downshifting.
As disclosed in the publication, however, after the transmission has completely downshifted the brake control device resumes to apply braking force as applied before the transmission starts to downshift, and decrements the braking force. As such, the engine braking increased by downshifting and the braking force applied by the braking force application controller cause a relatively large deceleration. Accordingly the vehicle's occupant(s) feels/feel physical impact, and furthermore, as the completion of the downshift is followed by decrementing an amount of braking force applied, despite the downshift, reduced braking force is provided, and after the downshift when a prediction is made that the transmission again downshifts, incremented deceleration is provided, so that despite the same transmission gear, deceleration is increased and decreased and the occupant(s) may feel uncomfortable.